The current invention is concerned with the field of packaging and interconnection of electronic components. More specifically, it deals with a method of converting electronic components packaged using ball grid arrays (BGAs) to a column grid array (CGA) form.
Many modern electronic components, for example, processor chips, have very large pincounts. These large pincounts are due to needs to interface with many other devices, processor word sizes (number of bits per each unit of information to be communicated to or from another device), and the like. When pincounts were smaller, more mature technologies, like wire bonding and tape bonding, were commonly used to perform the interconnection function. However, more recent devices with larger pincounts have caused manufacturers to resort to different technologies.
Among the more popular ways of dealing with the problems involved in providing connections for large-pincount devices is to use the ball grid array (BGA) technique. In a BGA, a small solder ball is bonded, during manufacture, to each contact point (pin) of the component. The balls provide a convenient way of then connecting the component to external leads.
FIGS. 1a and 1b show a representation of what such a BGA might look like. In FIG. 1a, a top view of a device packaged with BGA interconnects, device 1 is provided with an array of conductive balls 2 (made of solder and/or other conductive materials). Each of the balls is connected to a contact point of the device to provide an interconnection to another component (other device, power supply, ground, etc.). FIG. 1b shows a side view of the device shown in FIG. 1a. 
Another way of providing interconnects for large-pincount devices is using column grid arrays (CGAs). In a CGA, a small column of solder is bonded, during manufacture, to each contact point (pin) of the component. The columns serve the same purpose as the balls in a BGA. FIG. 1c shows a side view of what the device of FIG. 1a packaged in a BGA configuration might look like if, instead, it were packaged in a CGA configuration. Note that each ball 2 is replaced with a column 2xe2x80x2 to form the CGA package.
BGA electronic modules have become quite prevalent in the commercial electronics industry, and many useful devices are packaged in this manner. In some industry sectors, such as aerospace, military, and satellite communications, however, BGA packaging is not always the best packaging method. In particular, in such applications, BGA packaging does not offer the life and reliability required, due to the fact that, because of their relatively low height, the balls of a BGA are not pliant enough to absorb the differential expansion, during thermal expansions and contractions, between the device and a circuit board to which it is connected.
In such applications as aerospace, military, and satellite communications, CGAs, which, as discussed above, use columns instead of balls, are favored. Columns are taller than balls and are, therefore, more flexible and can absorb the difference in expansions and contractions between the device and the circuit board by bending, instead of cracking, as is often the case with balls.
A problem that commonly arises is that a component manufacturer will choose to package the component only one way, either in BGA or CGA form. Typically, a manufacturer producing a component in large quantities in BGA form will be unwilling to produce the same component, generally in limited quantities, in CGA form, for economic reasons. Hence, it would be desirable for the industry sectors in which CGA packaging is needed to be able to purchase components in BGA form and to convert them to CGA form.
One feature of the invention is to provide a process by which devices normally packaged in BGA form can be converted to CGA form.
Another feature of the invention is to provide CGA-packaged devices from BGA-packaged devices using the aforementioned process.
The inventive process, most simply stated, is to remove the balls from a BGA-packaged device and to replace them with columns to produce a CGA-packaged device. In one exemplary embodiment, the inventive process for removing the balls from a BGA-packaged device and replacing them with columns to produce a CGA-packaged device is achieved through the following steps:
heating a BGA module such that the material comprising the balls in the BGA melts;
brushing off the ball array surface to remove the balls; and
joining columns to the I/O pads.
In another exemplary embodiment, solder flux is applied to the ball array surface prior to brushing off the surface to remove the balls.
In yet another exemplary embodiment of the invention, a step of dressing the I/O pads is performed after the balls have been removed. This may be done, for example, via the steps of applying further solder flux and brushing.
In further exemplary embodiments, the aforementioned inventive CGA-packaged device is one produced via the inventive method, and a similar inventive method is used to replace the columns of a first CGA module with new columns, to obtain a second CGA module.
These and other features of the invention will become apparent in the detailed description below.